LeetCode89 Gray Code

问题来源LeetCode89

问题描述

Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0.

For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:

00 - 001 - 111 - 310 - 2

Note:
For a given n, a gray code sequence is not uniquely defined.

For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.

For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.

问题分析

Gray Code（格雷码）具体的用途可以看一下百度百科。一般格雷码有专门的迭代公式。

n位格格雷码=

最高位0 + n-1位格雷码的顺序 +

最高位1 + n-1位格雷码的逆序。

最高位0不影响大小，最高位1可以通过位运算来实现。1 << (n-1)

代码如下

public List<Integer> grayCode(int n) {        List<Integer> result = new ArrayList<>();    result.add(0);    if(n==0){        return result;    }    List<Integer> tmp = grayCode(n-1);    int addNumber = 1 << (n-1);    result = new ArrayList<Integer>(tmp);    for(int i=tmp.size()-1;i>=0;i--) {        result.add(addNumber + tmp.get(i));    }    return result;}

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GitHub地址 https://github.com/yanqinghe/leetcode

CSDN博客地址 http://blog.csdn.net/yanqinghe123/article/category/7176678